SPC Feb 19, 2018 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0148 PM CST Mon Feb 19 2018
Valid 192000Z - 201200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON THROUGH TONIGHT ACROSS PARTS OF THE SOUTHERN PLAINS...
...SUMMARY...
A few strong to severe thunderstorms are possible over a portion of
the Southern Plains, mainly late this afternoon into tonight.
...Discussion...
The previously issued outlook forecast reasoning appears on track.
Only a slight adjustment southward of the northern bound of the 2%
tornado probabilities were made near I-40 in OK.
..Smith.. 02/19/2018
.PREV DISCUSSION... /ISSUED 1029 AM CST Mon Feb 19 2018/
...Southern Plains to the MS Valley through tonight...
An amplified large-scale pattern with a western trough and eastern
ridge is now established and should persist for the next several
days. An expansive warm sector is in place from the mid MS Valley
and southern Plains to the Gulf Coast, with boundary-layer dewpoints
ranging from near 60 F north to the upper 60s along the coast. This
moist warm sector is supportive of clusters of slightly elevated
convection in multiple clusters, primarily focused along the
low-level jet corridor where warm advection is maximized from OK to
MO. Conditionally unstable midlevel lapse rates (around 7 C/km) and
the low-level warm/moist advection will continue to support elevated
thunderstorms through the period, though clouds will tend to limit
surface heating from eastern/northern OK northeastward along a
slow-moving front.
Some cloud breaks are more probable this afternoon from western OK
into northwest TX, where surface heating will boost MLCAPE values
into the 1000-1500 J/kg range with only weak convective inhibition.
However, forcing for ascent will also be weak at best along the
dryline south of the triple point near I-40 along the OK/TX border,
and storm initiation is somewhat in question. If isolated storms do
form this afternoon/evening, buoyancy and vertical shear will be
sufficient for supercells capable of producing large hail and
perhaps an isolated tornado. The odds for storm development should
increase later this evening through tonight from southwest/central
TX into central OK, as an embedded shortwave trough (now over Baja)
ejects northeastward and interacts with the unstable warm sector.
Embedded supercells and/or short bowing segments will be possible,
with an associated threat for isolated large hail/damaging winds, as
well as an isolated tornado. Will maintain the low severe
probabilities in this update, but there will still be some potential
for an upgrade in later outlook updates across parts of TX/OK.
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